1. Field of the Invention
The present invention relates to a process for preparing a molded form of oriented polyimide essentially consisting of a specific polyimide.
2. Description of the Related Art
In order to obtain oriented polyimide forms by stretching primary molded forms such as fibers, films, sheets and bars which are consisting of thermoplastic polyimide, it is required in a stretching step to maintain the primary-molded forms and stretching equipment at high temperatures, for example, from 250.degree. to 400.degree. C. Particularly in the case of stretching a specific polyimide of the present invention having a glass transition temperature of about 250.degree. C. and a melting point of about 380.degree. C., the resin is required to maintain the temperature at least its glass transition temperature. The equipment for molding at such temperature is very difficult to uniformly heat. Further, complete heat-insulation of the stretching equipment is difficult and it is unfavorable in economy to uniformly maintain high temperatures for a long time. Stretching can also be conducted at temperatures below the glass transition point. However, breakage of molecular chains and microvoids unfavorably occur.